Drawing instrument.



D. S. CLARK DRAWING INSTRUMENT.

APPLICATION FILED APB..15, 1908. 924,734, Patented June 15, 1909.

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APPLICATION FILED APR. 15, 1908.

Patented June 15,1909;

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UNITED STATES PATENT OFFICE.

DAVID S. CLARK, OF DETROIT, MICHIGAN.

DRAWING INSTRUMENT.

To all whom it may concern:

Be it known that I, DAVID S. CLARK, a citizen of the United States of America, residing at Detroit, in the county of Wayne and State of Michigan, have invented certain new and useful Improvements in Drawing Instru ments, of which the following is a specification, reference being had therein to the accompanying drawings.

This invention relates to drawing instruments and especially to a combined railroad curve and protractor adapted to be raised to give a curve of any degree, and consists in the matters hereinafter set forth, and more particularly pointed out in the appended claims.

In the drawings, Figure 1 is a plan view of an instrument embodying features of the invention. Fig. 2 is a view in section on or about line ma: of Fig. 1. Fig. 3 is a view of the outer side of the curve. Fig. 4 is a view in detail of a radius rod stud. Fig. 5 is a diagram showing method of plotting guide slots for radius rod studs.

Referring to the drawings, 1 indicates a flexible ribbon or spline of spring material and uniform section tangentially secured at its center by a stud 2 or the like against the rounded apex of a thin, substantially triangular base or guide plate 3 of metal, hard rubber or like suitable material, which is flush with the lower edge of the spline. A slide plate 4 of suitable material is movably secured on the base by a pair of studs 5 on the base plate engaging a slot 6 in the slide coincident with a line perpendicular to the tangent of the apex at the point of attachment of the spline, said line being the major axis of the base, an index plate 7 on the studs and thumb screw 8 acting as a clamp to secure the plates when set as desired. The outer ends of a plurality of radius rods 9 are hinged or pivoted at regular intervals to the spline in symmetrical relation to the center stud 2. Studs 10 or other suitable connecting means at the other end of the rods each engage a groove 11 in the slide and a slot 12 in the base at their point of intersection, the slot being rabbeted on the underside to receive the stud. The loci of the slots and grooves are readily determined as shown in Fig. 5. A series of curves of different degrees whose outer one 18 and inner one 14 are the limits of the range of action of the instrument are Specification of Letters Patent.

Application filed April 15, 1908.

Patented June 15, 1909.

Serial No. 427,152.

The radii 15 are likewise drawn. By locating points on the radii which correspond to the inner ends of the radius rods, the base slot loci 17 are readily plotted, and the coordinates a placed and similarly the intersections of the thus located coordinates a and abscissas a; which are stepped off at distances corresponding to the spacing of the several curve centers give the groove loci 18.

The slide 4 is graduated along the edge of the slot 6 so that a curve of any degree desired may be obtained by bringing the index plate 7 into register with the proper degree mark on the slide and clamping the plates together by the thumb screw 8. The outer radius rods have braces 19 thereon supporting an extension of the spline beyond each rod rigidly at right angles to the rods for tangents.

The studs 10 are removable so that slide plates giving different ranges of action may be interchangeably used although for field work a very wide range may be obtained by extending the plates suficiently. The outer face of the spline may also be graduated for use as a protractor when the slide is set at one point, as for example, for a 10 degree curve.

One feature of the invention is the wide range obtainable in a single instrument, that thus replaces the sets of curves now common for railroad and map work. Another advantage is the direct reading of the instrument so that it can readily be used without aid of a radius table. Furthermore it is especially adaptable for field work where quick adjustment is desirable.

Obviously changes in the details of construction may be made without departing from the spirit of the invention and I do not limit myself to any particular form or arrangement of parts.

What I claim as my invention is 1. A drawing instrument comprising a substantially triangular base plate, a flexible spline tangentially secured between its ends to the apex of the plate, a slide plate reciprocable on the base parallel to the major axis thereof, and radius rods pivoted at intervals at their outer ends to the spline in symmetrical relation to the major axis of the base, said plates having guides formed therein in engagement with the inner ends of the radius rods adapted to hold the rods condescribed as shown on the predetermined l vergent to a common center.

scale, usually that of 100 feet to one inch.

2. A drawing instrument comprising a substantially trian ular base plate, a flexible spline tangentially secured between its ends to the apex of the plate, a slide plate reciprocable on the base parallel to the major axis thereof, radius rods pivoted at intervals at their Outer ends to the spline in symmetrical relation to the major axis of the base, said plates having guides formed therein in engagement with the inner ends of the radius rods adapted to hold the rods convergent on a common center, and a brace on each of the outer rods adapted to hold the spline beyond each of said rods rigidly at right angles thereto.

3. A drawing instrument comprising a substantially triangular base plate having a rounded apex, a flexible spline of spring ma terial tangentially secured between its ends against the apex, a slide plate having a central guide slot coincident with the major axis of the base plate, clamping guiding means on the base engaging the guide slot, andradius rods pivotally secured at their outer ends to the spline at intervals in symmetrical relation to the major axis of the base, said plates having guides formed thereinin sliding engagement with the inner ends of the rods adapted to hold the rods substantially in radial relation to the spline in convergence on its shifting center of curvature.

4. A drawing instrument comprising a substantially triangular base plate provided with slots, a flexible spline tangentially secured between its ends to the apex of the plate, a slide plate reciprocable on the base parallel to the major axis thereof, radius rods pivoted at intervals at their outer ends to the spline in symmetrical relation to the major axis of the base, said slide having pairs of grooves each crossing a slot in the base, the inner ends of the rods each having sliding engagement with a groove and slot at their intersection, and said slide and base being adapted when moved on each other to swing the rods in and out in radial relation to the spline and in convergence on its shifting center of curvature.

5. A drawing instrument comprisinga substantially triangular base plate, a flexible spline tangentially secured between its ends to the apex of the plate, a slide plate reciprocable on the base parallel to the major axis thereof, and radius rods pivoted at intervals at their outer ends to the spline in symmetrical relation to the major axis of the base, the plates having guides formed therein in sliding engagement with the inner ends of the radius rods that are adapted to hold the rods in radial relation to the spline convergent on its shifting center of curvature when the plates are moved on each other,

and the spline being graduated to read als a protractor when the plates are in predetermined position. g

In testimony whereof I my signature in presence of two witnesses.

DAVID s. CLARK.

Vvitnesses V O. R. STIQKN Y, OTTO F. BARTHEL. 

